Geologic CO2 Storage Potential

Geologic CO2 storage involves the capture of anthropogenic CO2 before it is released to the atmosphere and injecting it into deep underground rock layers (geologic formations). These formations can include oil and gas reservoirs, geologic layers that contain very salty water (brine or saline formations), and coal beds that are too deep to mine.

Major Regional Sedimentary Basins

Sedimentary basins are made up of thick accumulation of sandstone, shale, and limestone that offer good combinations for CO2 storage. Within the PCOR Partnership region are eight sedimentary basins. These basins have been well characterized during commercial oil and gas activities and are known to offer good potential for CO2 storage. The geologic characteristics that are necessary for suitable storage vary regarding the specific location, but many areas meet the following minimal requirements: Sedimentary Basins
  • Be capable of holding CO2 in place for a long period of time (for example, a seal above a permeable zone of rock similar to the situation that would trap and store oil or natural gas).
  • Be isolated geologically from underground sources of drinking water.
  • Have suitable storage zone layers at depths greater than 2600 feet (800 meters) to ensure that the stored CO2 is in its dense physical phase (storage in coal can be shallower).
  • Be in a stable area not prone to earthquake activity.
  • Have formation water salinities greater than 10,000 mg/L.1
Click to enlarge

Oil and Gas Reservoirs

Oil and Gas Fields Because of their demonstrated ability to hold fluids, oil-bearing zones are excellent candidates for CO2 storage. In addition, the fields are well understood and there is significant field infrastructure already in place. As a benefit, when CO2 is injected into a mature oil field, it may produce additional oil through a process known as CO2 enhanced oil recovery (EOR). EOR is an attractive option for carbon capture and storage (CCS) because the costs associated with CCS are offset by the revenue from recovery of additional oil.1

Estimates developed by the PCOR Partnership indicate that the oil and gas fields of the region have the capacity to safely and effectively store over 3.2 GT of CO2.2 Click to enlarge

Saline Formations

Saline Formations Deep saline formations are layers of porous rock that contain waters with salinity greater than 10,000 mg/L total dissolved solids (TDS). This water is generally unsuitable for drinking or agriculture. Saline formations are very promising as potential CO2 storage sites because they are often thicker and more a really extensive than oil and natural gas reservoirs or coal seams and therefore represent an enormous potential for storage.

Within the PCOR Partnership region, there are 13 deep saline formations. Each has the potential to store large quantity of anthropogenic CO2. Together, these saline formations are estimated to have the capacity to store between 368 and 1220 billion tons of CO2.1  Click to enlarge

Unminable Coal

Coal Storage CO2 could potentially be stored in unminable coal seams. Unminable coal refers to coal seams that are too deep or too thin to be economically mined. CO2 injected as a gas into a coal seam will adsorb onto the coal surface and be stored.

All coal seams have varying amounts of methane (natural gas) adsorbed onto pore surfaces and if enough methane is present under the proper conditions, coalbed methane (CBM) can be recovered by drilling wells into coal seams. Injecting CO2 into the coal seam has the potential to produce otherwise unavailable natural gas while storing the CO2. This process is called enhanced coalbed methane (ECBM) recovery. Producing coalbed methane could help offset the cost of the CO2 storage operation. Click to enlarge

The PCOR Partnership region has three major unminable coal formations that have been characterized with respect to CO2 storage: Ardley coal zone in the Alberta Basin, Harmon–Hanson interval in the Williston Basin, and Wyodak–Anderson Formations bed in the Powder River Basin. The total maximum CO2 sequestration potential for all three coal horizons is approximately 8 billion tons. 1 


References:
  1. Glazewski, K.A., Grove, M.M., Peck, W.D., Gorecki, C.D., Steadman, E.N., and Harju, J.A., 2015, Characterization of the PCOR Partnership Region : Plains CO2 Reduction (PCOR) Partnership topical report for U.S. Department of Energy and multiclients, Grand Forks, North Dakota, Energy & Environmental Research Center, January.
  2. Peck, W.D., Buckley, T.D., Battle E.P., and Grove, M.M., compilers and creators, 2017, Plains CO2 Reduction (PCOR) Partnership atlas (5th ed., rev.): Prepared for the U.S. Department of Energy National Energy Technology Laboratory and the PCOR Partnership, Grand Forks, North Dakota, Energy & Environmental Research Center, 126 p.